Electric circuit interrupter



24, 1950 R. J. BASKERVILLE 2,938,095

ELECTRIC cmouxr INTERRUPTER 3 Sheets-Sheet 1 Filed Oct. 1, 1958 I I I II I I I IIIIIIIIIIIII Inventors,

Ralph J. Baskerville,

by. His Attorney.

May 24, 1960 R. J. BASKERVILLE ELECTRIC CIRCUIT INTERRUPTER 3Sheets-Sheet 2 Filed Oct. 1, 1958 Inventor. falph J. Baskerville u '7.

$5 At orneg 1959 R. J. BASKERVILLE 2,938,095

ELECTRIC CIRCUIT INTERRUPTER Filed Oct. 1, 1958 3 Sheets-Sheet 3lnventor-z Ralph J. Baskerville by WM His Atborrleg.

United States Patent O 2,938,095 ELECTRIC CIRCUIT INTERRUPTER Ralph J.Baskerville, Drexel Hill, Pa., assignor to General Electric Company, acorporation of New York Filed Oct. 1, 1958, Ser. No. 764,641 13 Claims.(Cl. 200-164) This invention relates to electric circuit interrupters orbreakers, and more particularly it relates to an improvement in thecontact structure of a low voltage air circuit breaker.

It is a well known practice in designing the contact structure ofcircuit interrupters to provide for scrubbing or wiping action betweenthe cooperating contact surfaces of the movable and relativelystationary contact members, respectively. This action, which serves tokeep the contact surfaces clean and improve breaker operation, isusually obtained by designing the contact structure so that there isrelative translational movement between the cooperating contact surfacesas the movable contact member moves from a position of initialengagement with the relatively stationary contact member, wherein thecooperating surfaces just touch, to a final, fully closed position. Itis an object of the present invention to provide a relatively simple andinexpensive circuit breaker contact structure having means forconveniently and accurately adjusting the position of the movablecontact member with respect to the relatively stationary contact member,whereby the desired amount of contact wiping action can be readilyobtained with great precision.

A general object of the invention is to provide an improved circuitbreaker contact structure of the character described hereinafter.

In carrying out my invention in one form, an electric circuit breaker isprovided with a relatively stationary contact member, and a cooperatingmovable contact member is pivotally supported for rotation about an axisbetween open and closed circuit positions with respect to the stationarycontact member. A generally cylindrical shaft disposed substantiallyparallel to the axis of rotation is rotatably connected to the movablecontact member. The shaft has an eccentric portion of polygonal crosssection, and an actuating member is adjustably coupled to this eccentricportion in order to move the movable contact member between its open andclosed circuit positions. The adjustable coupling between the eccentricportion of the shaft to two or more different predetermined angularpositions and the actuating member is arranged to permit controlledrotation of the shaft for precisely determining the closed circuitposition of the movable contact member, whereby the amount of contactwipe between the movable and relatively stationary contact members maybe varied.

My invention will be better understood and its various objects andadvantages will be more fully appreciated from the following descriptiontaken in conjunction with the accompanying drawings in which:

Fig. 1 is a side elevation of a circuit breaker contact structureembodying a preferred form of my invention, with the movable contactmember shown in its closed circuit position;

Fig. 2 is a front elevation of the contact structure illustrated in Fig.l, with the movable contact member moved to its open circuit position;

. 2,938,095 Patented May 24, 1960 by means of which actuating force istransmitted to the movable contact member; and

Fig. 6 is a view similar to Fig. 5 illustrating an alternativeconstruction of the impelling shaft of the contact structure.

Referring now to Fig. 1, I have shown an electric circuit breaker orinterrupter comprising a base member 11, a relatively stationary contactmember 12 mounted on the base, an electroconductive bracket 13 mountedon the base in spaced relation to the stationary contact member, amovable contact member 14 pivotally supported by bracket 13 and disposedin cooperative relationship with the stationary contact member 12, andactuating means such as a crossbar 15 coupled to the movable contactmember 14 for moving this member into and out of circuit-makingengagement with the stationary contact member 12. The components 12, 13and 14 comprise the contact structure of one pole unit of an alternatingor direct current circuit breaker or interrupter, and other similar poleunits (not shown) can be mounted for gang operation on the base member11 adjacent to the pole unit that has been illustrated in Figs. 1 and 2.

The base member 11 supports the current-conducting studs of the breakerand the other breaker parts directly connected to the studs. Asillustrated in Fig. l, the base member comprises a sheet 16 of electricinsulating material of substantially uniform thickness. The sheet 16 isshaped to form a channel-shaped section or depression at 17, and thebottom of this section is provided with an aperture for snugly admittingand partially supporting an upper breaker stud 18. For the purpose ofthe present description, the contact structure 12-14 will be consideredmounted on the front of the base 11, and the upper breaker stud 13 isconnected to a suitable electric power source or bus (not shown) locatedbehind or to the rear of the base. The contact structure shown in thedrawings and described herein to illustrate a preferred embodiment of myinvention is designed for connection to an electric power bus rated 600volts A.C. and capable of supplying as much as 25,000 amperesshort-circuit current.

The stationary contact member 12 is mounted on the upper breaker stud18. As can be seen in Fig. 1, the upper stud 18 is secured to the sheet16 of base member 11 by suitable support means such as generallyL-shaped angles 19 and 20. The angles 19 and 20 are respectivelydisposed above and below stud 18 and are fastened thereto by threecopper rivets or the like. The lower angle 20 is provided with a pair oftapped holes, and a pair of appropriate bolts 21 is used to secure thisangle to the base member 11. The supporting angle 19, which extendsabove the breaker stud 18 as is shown in Fig. 1, serves as aconventional arc runner in cooperation with the stationary contactmember 12. This angle is provided with a stud 22 for securing it to theinsulating sheet 16 of the base 11.

The end of breaker stud 18 extending forward from the base member isdivided into two horizontally diverging branches, whereby this stud inplan view has a general ly Y-shaped appearance. In the preferredembodiment of my invention illustrated in Figs. 1 and 2, the stationarycontact member 12 comprises at least one pair of elongated contaotelements or fingers 23, each finger 23 being pivotally supportedintermediate its ends on the outer end of a different diverging branchof the breaker stud 18. For this purpose, the outer ends of thediverging contact surfaces 24 normally disposed in branches arerespectively provided with generally cylindrical bearing surfaces havingcenterlines oriented inv a vertical direction as viewed in Figs. 1 and2. Each hearing surface is recessed so that Shoulders are formed at itsupper and lower ends to prevent vertical movement of the associatedcontact finger. If desired, the length of the bearing surface can bemade suflicient to accommodate more than one contact finger 23 inside-by-side rel ation.

The bearing surfaces at the outer ends of the diverging branches of thebreaker stud 18 provide fulcrums for a pair of contact fingers 23, andthe pivotal connection between each contact finger and the breaker studforms a current-conducting joint. The fingers are respectively supportedon opposite bearing surfaces in opposing relationship with respect toeach other for pivotal movement in a common horizontal plane. Theopposing or inner ends of the contact fingers are movable in separate,relatively short arcuate paths, and the opposing ends are respectivelyprovided with generally flat, complementary a common vertical plane asviewed in Figs. 1, 2 and 4.

The inner end of each contact finger 23 has an extension 25 (see Fig. 4)disposed to engage a common stop 26 for determining the limit of thearcuate movement of the contact surface 24 in one direction. The stop26, as is indicated in Fig. 2, comprises a pin vertically disposedintermediate the divergent branches of the breaker stud 18 and fixedlyconnected to the upper and lower supporting angles 19 and 20. Associatedwith the outer end 27 of each contact finger 23 is suitable springmeans, for example, the illustrated tension spring 28 which may beanchored at one end to a fixed member such as pro- 'vided by a laterallyextending lug 29 of the upper supporting angle 19. Thus, spring means 28establishes a biasing torque in the contact finger 23 tending to movethe contact surface 24 along its arcuate path in a forward directionaway from the base member 11, and such movement by the finger is limitedby the stop pin 26.

The above-described structure provides for arelatively limiteddeflection of each contact finger in a rearward direction.

The biasing torque is opposed and overcome and each contact finger 23 ofthe relatively stationary contact member 12 is tilted slightly on itsfulcrum by the action of the movable contact member 14. As will be morefully explained hereinafter, the movable contact member 14 in theillustrated embodiment of the invention includes a pair of armsrespectively provided with contact surfaces 47 which move in parallelplanes disposed approximately perpendicular to the plane defined by thearcuate paths of the contact surfaces 24 of the fingers 23. Theactuating means 15 provides actuating force for moving each contactsurface of member 14 into and out of circuit-making abutting engagementwith the contact surface 24 of a different contact finger.

During a circuit making operation, the contact surfaces 47 of themovable contact member 14 are jointly carried rearwardly from their opencircuit position (Fig. 2) into substantially simultaneous engagementwith both of the cooperating contact surfaces "24, and further rearwardmovement of the contact surfaces 47 to their fully closed position (Fig.l) forces the spring means 28 to yield as the relatively stationarycontact fingers 23 tilt on their fulcrums. The arrangement is such thatthe cooperating contact surfaces 24 and 47 follow different paths. ofmovement while in engagement with each other. Consequently one of theengaging surfaces is translated with respect to the other and there willbe sliding or scrubbing movement therebetween. In this manner,conventional contact Wiping action is obtained, and the amount of wipingaction can be adjusted with great precision in accordance with myinvention soon to be described in detail.

- respectively,

Although for the sake of illustration I have shown and describedcooperating contact members constructed and arranged for abuttingcircuit-making engagement, I do not wish to be limited to such anabutting type contact structure. It will soon become apparent that thesuccessful application of my invention does not depend in any respect onthe particular nature of the cooperating relationship between themovable and stationary contact members. In lieu of the abuttingarrangement illustrated, the movable contact member could be, forexample, a blade-like member disposed to slide between and spread aparta pair of generally parallel cooperating contact elements.

In Figs. 1 and 2 it can be seen that the electro-conductive bracket 13for supporting the movable contact member 14 is mounted on base member11 by means of a pair of suitable bolts 30 or the like. The bracket 13has a lower lip 31 provided with a hole for the purpose ofconnecting asuitable current-conducting member or another breaker stud (not shown)to the bracket. Part of the bracket 13 is disposed adjacent the frontsurface of the insulating sheet 16 of base member 11, and a rigidreinforcing member 32 is disposed adjacent the rear surface of the sheet16 in overlapping relationship with bracket 13 and the lower supportingangle 20, respectively. The reinforcing member 32 is provided so thatthe loading of the insulating sheet 16 in the area between the bracket13 and the relatively stationary contact member 12 will be incompression rather than in flexure. A channel 33 of insulating materialis disposed intermediate the reinforcing member 32 and the rear of sheet16 to provide additional electrical insulation between the sides ofmember 32 and the fastening bolts 21 and 3G.

The bracket 13 includes a pair of spaced-apart upstanding lugs 34 and 35projecting in front of base member 11. A removable pivot pin 36 issupported by the lugs 34 and 35, the axis of the pivot pin extending ina horizontal direction generally parallel to the plane of the basemember 11 as viewed in Figs. 1 and 2. The pivot pin 36, which passesthrough both of the lugs 34 and 35 and protrudes from their outwardlyfacing sides, is retained in place by a releasable clamp 37 connected tothe pin intermediate the lugs. The clamp 37 preferably comprises aresilient helical coil loosely encircling pin 36, the length of thehelix corresponding approximately to the span between the lugs 34 and35. The opposite ends of the coil of clamp 37 extend tangentiallytherefrom and are arranged for movement between first and secondcooperating positions. In Fig. 2 the ends are shown in a positionwherein they releasably engage each other, and in this self-lockedposition the circumference of the coil is contracted for firmly graspingthe encircled pin and preventing axial movement and removal thereof. Byseparating the ends and permitting them to assume their other positionin accordance with the resilience of the coil, the circumference of thecoil can be expediently expanded for assembling or disassemblingpurposes.

The connection between the movable contact member 14 and the supportingbracket 13 will now be de scribed with particular reference to Figs. 2and 4. The movable contact member 14 comprises a pair of elongatedcontact arms 38 and 39 arranged in generally parallel relation for jointoperation. One end 40 of the arm 38 is disposed adjacent the outwardlyfacing side of the upstanding lug 34 and is rotatably mounted on aprotruding portion of pivot pin 36; and one end 41 of the other contactarm 39 is disposed adjacent the outwardly facing side of lug 35 forrotatable mounting on the opposite protruding portion of the pivot pin.

The connection between each movable contact arm 38, 39 and theelectroconductive bracket 13 is arranged to provide three separatecurrent-conducting joints. The first such joint is provided by thebearing surfaces between the contact arm and the pivot pin 36 on whichthe movable contact arms it rotates, that is, between pin 36 and theperiphery of a hole 42 which has been located in the one end 40, 41 toaccommodate the pin 36. The surface of the pivot pin 36 and theperiphery of hole 42 may be silver plated and burnished to ensure awear-resistant, low electric resistance current-conducting path.

The second current-conducting joint is obtained by providing theoutwardly facing side of each lug 34, 35 of the bracket 13 with asubstantially fiat, smooth slide surface 44 disposed generallyperpendicular to the axis of the pivot pin 36. Each slide surface 44 iscontiguous to a smooth, pertaining slide surface 45 provided on therelatively broad inner side of the pivoted end 40, 41 of each movablecontact arm 38, 39, i.e., on the side of the contact arm facing thesupporting bracket 13. Each slide surface 45 is disposed generallyparallel to the respective adjoining slide surface 44 of the bracket 13,and therefore all of the slide surfaces 44 and 45 are substantiallyperpendicular to the axis of pivot pin 36 which corresponds to the axisof rotation of the movable contact arms 38 and 39.

The slide surface 45 of each movable contact arm includes a raisedsection which, as can best be seen in Figs. 3 and 4, preferablycomprises a portion of a cylinder. The crest of this raised section isoriented so that it extends in a direction substantially perpendicularto the longitudinal centerline of the contact arm, and it is intersectedby the hole 42 provided for pivot pin 36. The crests of the raisedsections of the two slide surfaces -45 respectively cooperate with andare contiguous to the .slide surfaces 44 of bracket 13, and pivotalmovement .of the contact arms on pin 36 causes each crest to slide voverthe associated slide surface of the relatively staztionary bracket 13.The contiguous portions of each ;pair of cooperating slide surfacesdefine a line contact which provides the second current-conducting jointbetween each movable contact arm and the supporting ibracket. Of course,as an alternative to the specific .arrangement illustrated and describedaboev, a raised :section could be located on each of the slide surfaces44 and the slide surfaces 45 could be made substantially zflat.

Contact pressure at the joints formed by the respective ,pairs ofcontiguous slide surfaces 44 and 45 is maintained by means of anelectroconductive spring member 46 which preferably comprises a U-shapedspring clip. As indicated in Figs. 1 and 2, the resilient upstandinglegs of the clip 46 are split for respectively bearing against :theouter sides of the pivoted ends 40 and 41 of the :contact arms 38 and 39at points disposed on opposite :sides of the pivot pin 36. Theelectroconductive spring :member 46 is secured to the bracket 13, andsince it also is in engagement with each movable contact arm it providesthe third current-conducting joint. In addition, spring member 46applies a sidewise force which maintains contact pressure at thecontiguous surfaces of both pairs of cooperating slide surfaces 44 and45. This force is supplemented by an electromagnetic force whenever themovable contact member 14 is conducting current. Whenever the parallelcontact arms 38 and 39 conduct alternating current, a magnetic force isestablished tending to reduce the spacing between these two arms andthereby establishing additional contact pressure at the contiguous slidesurfaces, the magnitude of this sidewise force being proportional to thesquare of the current magnitude.

The diameter of the hole 42 in the pivoted ends of is made slightlygreater than the diameter of pivot pin 36. This arrangement permits thecontact arms 38 and 39 to rock on pivot pin 36. The crests of the raisedsections of the slide surfaces 45 provide fulcrums for the rockingmovement of the arms 38 and 39, respectively. This arrangement allowsfor 'a certain degree of misalignment of the various parts and a liberalmanufacturing tolerance without adversely 6 affecting the positivenessof the electric contact between the movable elements and the supportingbracket 13.

By utilizing three parallel current-conducting joints for each of thetwo parallel arms'of the movable contact member 14, the overall electricresistance of the pivotal connection has been efficiently reducedthereby significantly decreasing temperature rise. In this manner, it ispossible to obtain a successful contact structure without theconventional flexible braids or conductors.

In the illustrated embodiment of my invention, the corresponding freeends of the contact arms 38 and 39 are provided respectively withtransverse contact surfaces 47 disposed for abutting engagement with thecontact surfaces 24 of the relatively stationary contact fingers 23.Rotary movement of the contact arms on pivot pin 36 carries the contactsurfaces 47 through arcuate paths which define vertical planesintersecting at approximately right angles the horizontal plane ofmovement of the relatively stationary contact surfaces 24, as viewed inFigs. 1, 2 and 4. This arrangement permits the convenient utilization ofmore than one stationary contact finger for each movable contact arm,whereby more than two separate points of circuit-closing engagement canbe provided between the movable contact member 14 and the relativelystationary contact member 12.

The cooperating contact surfaces 24 and 47 preferably are made of silvertungsten carbide material which will successfully perform the continuouscurrent-carrying function of the contacts and also the required circuitmaking and breaking duty, without appreciable contact erosion or pittingor contact welding as a result of electric arcing. Therefore it is notnecessary to provide separate arcing and main contacts. With the variousparts shown in Figs. 1 and 2 appropriately dimensioned, the contactstructure will safely carry at least 225 amperes continuously at 600volts A.C., and the same contact structure can be modified to carry atleast 600 amperes continuously merely by changing the relativelystationary contact member 12 so that two additional contact fingers 23are respectively disposed adjacent those shown and by appropriatelyextending the contact surfaces 47 of the movable contact arms.

In order to obtain a compact arrangement at the cooperating contactsurfaces 24 and 47, the contact arms 38 and 39 are spaced closertogether at their corresponding free ends than at the pivot pin 36. Asis shown in Figs. 2-4, this has been accomplished by axially offsettingthe free ends of the contact arms with respect to the pivotallyconnected ends 40 and 41, respectively. In other words, each free end isdisposed inside a plane normal to the pivot pin 36 that intersects thebearing area providing the pivotal connection between the associatedmovable contact arm (the periphery of hole 42) and pin 36. Thus, thecenter of the circuit-making surface area of the contact surface 47,that is, the center of the area of surface 47 which engages the contactsurface 24 of the stationary contact finger 23, defines with the centerof the pivotal connection to pivot pin 36 a straight line 48 whichintersects the axis of rotation (the axis of pivot pin 36) at an obliqueangle. See Fig. 3.

The contact arms 38 and 39 have been oppositely offset at intermediateportions 49. As is indicated in Figs. 3 and 4, the offset portion 49 isprovided with a transverse hole 50 the centerline of which is orientedparallel to the pivot pin 36. An actuating member such as a cylindricalimpelling shaft 51 is rotatably disposed in hole 50, and by this meansactuating force is applied to the movable contact member 14 for jointlymoving the contact arms 38 and 39 between open and closed circuitpositions. The offset portion 49 of each of the contact arms is soarranged that the line of action of the resultant actuating forceintersects the straight line 48. In other words, a common plane ofaction and reaction is defined by the center of the bearing surfacebetween the impelling shaft 51 and the offset portion 49 of the holes 50in the offset portions contact arm, the center of the pivotal connectionbetween pivot pin 36 and the pivoted end of the arm, and the center ofthe engaging area of contact surface 47. This plane will include theintersection of the respective planes of movement of the cooperatingmovable and relatively stationary contact surfaces 47 and 24. As aresult, there is no net component of actuating force having a moment armwith respect to the straight line 48, and there is substantially notorsion or twisting tendency in the contact arm in its closed circuitposition. Such a tendency would be undesirable because it would causeuneven forces along the length of the crest of the raised section ofslide surface 45 with respect to the contiguous slide surface 44,whereby the effectiveness of this current-conducting joint between themovable contact member 14 and the supporting bracket 13 would beseriously impaired.

In the vicinity of the offset portions 49 of the contact arms 38 and 39,protrusions 52 are formed. These protrusions 52, which preferably are inthe form of curved embossments on the inner sides of the contact arms,are respectively disposed to extend in overhanging relationship with thelugs 34 and 35 of bracket 13. In this manner, the current-conductingjoints formed by the two pairs of contiguous slide surfaces 44 and 45are shielded from the electric arc and are products which may beproduced during circuit breaking action of the contact structure. Theprotrusions 52 will prevent particles of foreign matter produced duringcircuit breaking action from entering these joints by straight-linepaths from the area of arc interruption. Such foreign matter, ifpermitted to enter the joint, could cause excessive wear and increasedcontact resistance.

The impelling shaft 51 fits relatively loosely in the 49 of the movablecontact arms 38 and 39, whereby each arm can slide on shaft 51whilerocking on pivot pin 36. Thus the contact surface 47 of each arm is freeto move in a lateral or transverse direction, and such lateral movementis controlled by resilient means associated with the contact arm. As isshown in Figs. 2 and 4, the resilient means preferably comprises ahelical spring 53 disposed on impolling shaft 51 intermediate thecontact arms 38 and 39. The spring 53 applies a transverse force to eachcontact arm and establishes in the arm a relatively weak biasing torquewith respect to the pivot provided by the line contact at the jointformed by the contiguous slide surfaces 44 and 45. This biasing torqueis in a direction tending to spread apart the contact arms. Suchmovement of each contact arm is stopped and its normal position isdetermined by a bushing 54 disposed on shaft 51 between a retaining ring55 or the like and the circular outer side of the offset portion 49 ofthe arm.

During circuitmaking action of the contact structure, each contactsurface 47 comes into abutting engagement with the contact surface 24 ofa relatively stationary contact finger 23, and as the cooperatingcontact surfaces wipe the contact finger 23 is tilted on its fulcrum inopposition to its biasing torque. The arrangement is such that atransverse force is supplied to contact surface 47 by contact surface 24as the contact finger 23 moves pivotally on its fulcrum. Due to theresilient means 53, the movable contact arm yields to thistransverse'force and the contact surface 47 is able to move laterallywhile following the arcuate path of the contact surface 24. As a result,the'relative movement or translation between the cooperating contactsurfaces 24 and 47 in this lateral direction is reduced, therebyreducing the amount of fric- 'tion between these cooperating surfacesand improving the performance of 'the contact structure.

:The movable contact member 14 is coupled to the actuating means orcrossbar by means of an actuating member 56 which is coupled to theimpelling shaft 51 and which preferably comprises a generally U-shapedlink securely fastened to the crossbar. Eachleg of the link56 isprovided with an extension 57 connected to the first and secondrelatively fixed positions.

pivot pin 36 as shown in Fig. 1, and thus the crossbar 15 is supportedfor pivotal movement by pin 36. The crossbar is connected to a circuitbreaker operating mechanism by means of another link 58 and a connectingmember 59. The operating mechanism, which has not been shown, may be ofany suitable type for moving the connecting member 59 in a generallyhorizontal direction (as viewed in Figs. 1 and 2) and therebyreciprocally moving the crossbar 15 about its pivot between As a resultof this action, a shoulder 60 of the actuating member or link 56 iscarried through a predetermined arcuate path with respect to pivot pin36.

As is clearly shown in Figs. 2 and 4, the impelling shaft 51, which isdisposed in generally parallel axial relationship to the pivot pin 36,has opposite end portions 61 extending laterally from opposite sides ofthe movable contact arms 38 and 39, respectively. In accordance with myinvention, each portion 61 is made eccentric with respect to thecylindrical body of shaft 51, and the eccentric portions 61 areadjustably coupled to the actuating member 56 in a manner permittingcontrolled rotation of the shaft. The adjustable coupling has beenobtained in the illustrated embodiment of the invention, for example, bymaking each eccentric portion 61 a polygon having at least two flatsides and by providing a slot in each leg of the actuating member 56 forreceiving the associated eccentric portion. As seen in Fig. 1, the twolengthwise sides of each slot in the actuating member 56 arerespectively defined by the shoulder 60 and by a. relatively stiffcantilever flat spring 62 which is carried by the member 56 in spacedreiation to shoulder 60 for resiliently bearing against the polygonaleccentric portion 61. In a preferred form of the invention, the crosssection of each eccentric end portion 61 of shaft 51 comprises anequiangular hexagon, and the parallel fiat sides of the hexagon arepositively but resiliently locked between shoulder 60 and the fiatspring 62. See Figs. 1, 5 and 6. Thus the slots in the actuating member56 permit controlled rotation of shaft 51, and the slots are disposedalso to permit radial movement of the eccentric portion 61 with respectto the axis of pivot pin 36.

By means of a conventional open-end wrench applied to the hexagonaleccentric portions 61, and without the necessity of disassembling orreassembling any parts, the impelling shaft 51 may be convenientlyrotated in steps of 60 degrees to any one of six different angularpositions disposed at intervals of 60 degrees. In each of these sixpositions, the movable contact member 14 is located in a differentrelative angular position with respect to the crossbar 15 and withrespect to the relatively stationary contact member 12. The purpose ofthis adjustrnent is to accurately establish the fully closed position ofthe movable contact member regardless of liberal manufacturingtolerances, whereby the desired amount of contact wipe can be preciselyobtained. More specifically, this adjustment is used to vary in inverserelationship the distances which the free end of each movable contactarm 38, 39 travels along its arcuate path from its open circuit positionto a point which circuit-making engagement with the relativelystationary contact member 12 is initially established and from saidpoint of initial engagement to its fully closed position, respectively,during a circuit closing operation of the contact structure. The totaldistance traveled by each free end between open and fully closedpositions will, of course, remain constant.

In order to obtain the six different angular positions of the movablecontact member 14 mentioned above, the eccentric hexagonal portions 61have been oriented in an unsymmetrical relationship with respect to adiameter 63 of the cylindrical body of shaft 51 that passes through thecenter e of the cross-section of eccentric portion 61. See Fig. 5. Inother words, the flats of the hexagonal portion 61 are not symmetricallydisposed with respect to diameter 63, and the maximum degree ofasymmetry has been obtained in the illustrated embodiment of myinvention by shifting each hexagonal portion fifteen degrees from asymmetrical position. As a result, the distance b from the axis ofrotation c of the cylindrical portion of shaft 51 to each flat side ofthe hexagonal portion measured along a line normal to the side isdifferent than the correspondingly measured distance from the axis toany other side, and accordingly the fully closed position of the movablecontact member 14 will be different for each of the six differentangular positions of the impelling shaft 51.

For the sake of expedient adjustment of contact wipe, it is desirable tovary the wipe in uniform steps. In other words, the position of themovable contact member 14 should be changed a uniform amount for eachdiscrete step in the adjustment process. With the constructionillustrated in Fig. 5, wherein the cross-section of the eccentricportion 61 of impelling shaft 51 is a regular or equal-sided hexagon,this desirable result is approached but not fully realized. Theconstruction illustrated in Fig. 6, however, enables the result to beobtained. Here the eccentric portion 61a of the shaft 51 has a hexagonalcross-section the sides of which are not equal in length and are notequidistant from the center e of the crosssection. The arrangement issuch that the normal distances (b) between the axis of rotation c of theshaft and the respective sides of the hexagon differ from each other bymultiples of a constant increment K, and consequently the amount ofposition change experienced by the movable contact member 14 is constantwhen the shaft 51 is rotated from one' angular position of shaft 51 toanother. The six normal distances in 'Fig. 6 have been identified inascending order of their lengths as follows: b b b b b and b and thesides of hexagonal cross-section are disposed in relation to the axis ofrotation c so that b =b +K, b =b +K or b =b +2K, etc.

As is clearly shown in Fig. 5, the impelling shaft 51 is constructed sothat the eccentricity of the hexagonal portion 61 (i.e., the distancefrom c to e) is less than the dimension d which is one-half the lengthof the fiat side of the hexagonal portion '61 and hence onetwelfth theperimeter of this portion. With this arrangement, the net effectivecrank arm of the eccentric portion 61 always lies within the limits ofthe flats so that the inherent tendency on the part of the impellingshaft 51 to rotate from the angular position to which it has beenadjusted is positively and successfully resisted. This proposition isillustrated in Fig. 5 where the vector F represents the resultant of theactuating force applied to the eccentric end portion 61 in order to holdthe contact structure closed and the vector R represents the resultantof the reactive force experienced by the impelling shaft 51. The neteffective cran'k arm of the eccentric portion 61 is equal to a for theparticular angular position of the impelling shaft 51 shown in Fig. 5.It will be apparent that the couple created by forces F and R cannot ofitself rotate the shaft 51 from the position shown as long as a is lessthan d.

The crossbar 15 may be extended across the width of the circuit breakerfor connection in a similar manner to other pole units of a multipolecircuit breaker. An isolating barrier 64 of insulating material is shownmounted on the crossbar 15 in Fig. 2. Other barriers 65 are provided forthe purpose of isolating the various current-conducting parts of theillustrated pole unit from the corresponding parts of adjacent poleunits and from ground. A suitable arc chute, not shown in the drawings,may be mounted on the base member 11 to enclose the cooperating contactsurfaces 24 and 47 for the conventional purpose of arc extinction.

While I have shown and described a preferred form of my invention by wayof illustration, many modifications will occur to those skilled in theart. Therefore, I con- 7 1O template by the concluding claims to coverall such modi fications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the base; abracket mounted on the base in spaced relation to the stationary contactmember; an elongated movable contact arm pivotally supported by thebracket for rotation about an axis, one end of the arm being disposedfor arcuate movement between open and closed circuit positions withrespect to the stationary contact member; a cylindrical shaft rotatablyconnected to the movable contact arm and disposed substantially parallelto said axis, the shaft having an eccentric, polygonal end portionextending laterally from said arm; and an actuating member movable in apredetermined arcuate path between first and second relatively fixedpositions and adjustably coupled to the end portion of the shaft formoving the one end of the contact arm between its open and closedcircuit positions, the adjustable coupling comprising a slot in saidactuating member for receiving said end portion and permitting radialmovement thereof with respect to said axis, one side of the slot beingdisposed resiliently to bear against said end portion thereby permittingrotation of the shaft for determining the closed circuit position ofsaid one end.

2. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the base; amovable contact member mounted on the base in spaced relation to thestationary contact member for pivotal movement about an axis betweenopen and closed circuit positions with respect to the stationary contactmember; an impelling shaft disposed substantially parallel to said axiscomprising a cylindrical portion rotatably connected to the movablecontact member and an eccentric portion having a hexagonalcross-section; and an actuating member reciprocally movable betweenfirst and second relatively fixed positions and adjustably coupled tothe eccentric portion of the impelling shaft for moving said movablecontact member between its open and closed circuit positions, theadjustable coupling being arranged to permit controlled rotation of theshaft to any one of six different angular positions thereby to determinethe closed circuit position of the movable contact member.

3. The contact structure of claim 2 in which the crosssection of theeccentric portion of the impelling shaft comprises an equiangularhexagon, whereby the six different positions to whichthe shaft can berotated are disposed at angular intervals of sixty degrees.

4. The contact structure of claim 2 in which the crosssection of theeccentric portion of the impelling shaft comprises an equiangular,equal-sided hexagon and in which the eccentricity of the eccentricportion is less than one-half the length of each side of the hexagon.

5. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the base; amovable cont-act member pivotally mounted on the base in spaced relationto the stationary contact member for movement between open and closedcircuit positions with respect to the stationary contact member; animpelling shaft comprising a cylindrical portion rotatably connected tothe movable contact member, the axis of rotation of said cylindricalportion being disposed substantially perpendicular to the plane ofmovement of the movable contact member, and an eccentric portion havinga hexagonal cross-section encompassing said axis of rotation, the sixsides of the hexagonal cross-section being disposed in relation to theaxis of rotation so that the distance from the axis to each sidemeasured along a line normal to the side is different than acorrespondingly measured distance from the axis to any other side;

and an actuating member reciprocallymovable between first and secondrelatively fixed positions and adjustably coupled to the eccentricportion of the impelling shaft for moving said movable contact memberbetween its open and closed circuit positions, the adjustable couplingbeing arranged to permit controlled rotation of the shaft to any one ofsix different angular positions thereby to vary the closed circuitposition of the movable contact member.

6. The contact structure of claim in which the sides of the hexagonalcross-section of the eccentric portion of the impelling shaft are notequidistant from the center of said cross-section and the normaldistances between the axis of rotation and the respective sides of thecrosssection differ from each other by multiples of a constantincrement.

7. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the base; abracket including a pivot pin mounted on the base in spaced relation tothe stationary contact member; a movable contact member comprising apair of generally parallel arms mounted for pivotal movement on thepivot pin, said arms having corresponding free ends disposed for jointarcuate movement between open and closed circuit positions with respectto the stationary contact member; a cylindrical shaft disposed ingenerally parallel axial relationship to the pivot pin and rotatablyconnected to both of the movable contact arms, the shaft having at leastone eccentric portion; and an actuating member pivotally connected tosaid pivot pin for movement between first and second relatively fixedpositions and adjustably coupled to the eccentric portion of the shaftfor pivotally moving. both of said movable contact arms.

8. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact comprising an electroconductivemember mounted on the base and a contact finger pivotally supported bysaid electroconductive member for relatively limited movement in anarcuate path; a bracket mounted on the base in spaced relation to thestationary contact; an elongated movable contact arm pivotally supportedby the bracket for movement at one end in an arcuate path, said armbeing disposed in relation to the contact finger so that the respectivearcuate paths define intersecting planes; a cylindrical shaft rotatablyconnected to the movable contact arm and disposed substantiallyperpendicular to the plane defined by the arcuate path of said one end,the shaft being provided with an eccentric portion extending laterallyfrom said arm; and an actuating member reciprocally movable betweenfirst and second relatively fixed positions and adjustably coupled tothe eccentric portion of the shaft for moving the one end of said armalong its arcuate path between open and closed circuit positions withrespect to the relatively stationary contact finger, the adjustablecoupling being arranged to permit controlled rotation of the shaftthereby to vary the length of the arcuate path from the open circuitposition of said one end to the stationary contact finger.

9. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact comprising an electroconductivemember mounted on the base, a contact finger pivotally suported by saidelectroconductive member for movement in a first plane, and spring meansfor establishing a biasing torque in the contact finger; a bracketmounted on the base in spaced relation to the stationary contact; anelongated movable contact arm pivotally supported by the bracket formovement at one end in a second plane substantially perpendicular to thefirst plane, the one end being disposed for circuit-making engagementwith said contact finger; resilient means associated with the movablecontact arm to permit transverse movement of said one end with respectto said second plane; a rotatable shaft, having an axis disposedsubstantially perpendicular to said second plane, loosely connected tothe movable contact arm and ineluding an eccentric end portion extendinglaterally from said arm; and an actuating member adjustably coupled tothe eccentric portion of the shaft for pivotally moving said arm, theadjustable coupling being constructed and arranged to permit controlledrotation of the shaft thereby to determine the amount of contact wipebetween the one end of said arm and the relatively stationary contactfinger.

10. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the basemember; an electroconductive bracket mounted on the base member inspaced relation to the stationary contact member; an elongated movablecontact arm pivotally connected to the bracket for rotation on an axis,one end of the arm being arcuately movable between open and closedcircuit positions with respect to the stationary contact member, theconnection between bracket and aim including contiguous slide surfacesdisposed generally perpendicular to the axis of rotation to form acurrent-conducting joint; a generally cylindrical shaft rotatablyconnected to the movable contact arm and disposed substantially parallelto said axis, the shaft having an eccentric portion; and an actuatingmember adjustably coupled to the eccentric portion of the shaft formoving said arm on said axis, the adjustable coupling being arranged topermit controlled rotation of the shaft thereby to determine the closedcircuit position of the one end of said arm. I

11. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the basemember; an electroconductive bracket mounted on the base member inspaced relation to the stationary contact member; an elongated movablecontact arm pivotally connected to the bracket for rotation on an axis,one end of the arm being arcuately movable between open and closedcircuit positions with respect to the stationary contact member, theconnection between bracket and arm including contiguous slide surfacesdisposed generally perpendicular to the axis of rotation to form acurrent-conducting joint, one of said surfaces being substantially fiatand the other surface being raised so that said current-conducting jointprovides a fulcrum for rocking movement by the arm with respect to theaxis; a cylindrical, rotatable shaft loosely connected to the movablecontact arm and disposed substantially parallel to said axis, the shafthaving an eccentric end portion extending laterally from said arm; andan actuating member reciprocally movable between first and secondrelatively fixed positions and adjustably coupled to the eccentricportion of the shaft for moving said am about said axis, the adjustablecoupling being arranged to permit controlled rotation of the shaftthereby to determine the closed circuit position of the one end of saidarm.

12. In the contact structure of an electric circuit inter rupter: abase; a bracket mounted on the base; a relatively stationary contactcomprising an electroconductive member mounted on the base in spacedrelation to the bracket and a contact finger pivotally supported by saidelectroconductive member for movement in an areaate path; a cooperatingmovable contact member con nected to the bracket for pivotal movementbetween open and closed circuit positions in a plane intersecting theplane defined by the arcuate path of said contact finger, the connectionbetween bracket and movable contact member including contiguous slidesurfaces disposed generally parallel to the plane of movement of themovable contact member to form a current-conducting joint; a cylindricalshaft rotatably connected to the movable contact member and disposedsubstantially perpendicular to the plane of movement of said movablecontact member, the shaft being provided with an eccentric portion; andan actuating member adjustably coupled to the eccentric portion of theshaft for pivotally moving said movable contact member, the adjustablecoupling being arranged to permit controlled rotation of the shaftthereby to determine the closed circuit position of said movable contactmember.

13. In the contact structure of an electric circuit interrupter: a base;an electroconductive bracket mounted on the base; a relativelystationary contact comprising an electroconductive member mounted on thebase in spaced relation to the bracket and a contact finger pivotallysupported by said member for movement in a first plane; a cooperatingmovable contact arm pivotally connected to the bracket for rotationabout an axis, one end of the arm being axially offset with respect tothe pivotal connection and being arcuately movable between open andclosed circuit positions in a second plane intersecting said firstplane, said one end having at least one contact surface engaging in theclosed circuit position at least one cooperative contact surface of therelatively stationary contact finger, the connection between arm andbracket and including contiguous slide surfaces disposed generallyparallel to said second plane to form a current-conducting joint, one ofsaid slide surfaces being substantially flat and the other slide surfacehaving a raised section defining with the fiat surface a line contact; acylindrical shaft rotatably connected to the movable contact arm anddisposed substantially perpendicular to said second plane, the arm beingconstructed and arranged so that the center of the bearing surfacesbetween shaft and arm together with the center of the engaging area ofthe contact surface of the arm and the centre of the pivotal connectionbetween arm and bracket are in a third plane disposed parallel to orincluding the intersection of said first and second planes, said shafthaving an eccentric portion extending laterally from the arm; and anactuating member adjustably coupled to the eccentric portion of theshaft for moving said arm about said axis, the adjustable coupling beingconstructed and arranged to permit controlled rotation of the shaftthereby to determine the closed circuit position of the one end of saidarm.

References Cited in the file of this patent UNITED STATES PATENTS

